1. Field of the Invention
The present invention relates to a device that detects and indicates operation force or pressure, and in particular to a force detector/indicator employing a piezoelectric element and a liquid crystal display.
2. Description of the Related Art
Conventionally, devices employing springs have been used for detecting and indicating operation force and pressure. As shown in FIG. 1, in one example of such a device an operation force or pressure P is applied to actuator 1 and the displacement of the tip of spring 3 centered on fulcrum 2 is indicated on scale 4.
Another example of the prior art employs a piezoelectric body to detect and indicate operation force or pressure P. As shown in FIG. 2, such a device indicates the voltage generated by the piezoelectric effect when an operation force or pressure P is applied to piezoelectric plate 5 by means of a pressure gauge, the circuit structure of which includes voltage amplifying circuit (AMP) 6, A/D conversion circuit 7, CPU 8 for calculating correction, indicator 9 for displaying a numerical value of the pressure, and power source 10 for driving these components.
Yet another example of the prior art indicates pressure applied directly against a liquid crystal display. As shown in FIG. 3, such a device is provided with liquid crystal display 14 composed of cylindrical retainer 11 holding liquid crystal layer 17 sandwiched between two glass plates 16a, 16b with reflective layer 15 applied to glass plate 16a, and arranged such that shaft 12 within retainer 11 is pressed against liquid crystal display 14 by spring 13, with the tip of shaft 12 protruding from retainer 11. In this type of liquid crystal display, when a pressure P is applied against the tip of shaft 12, pressure is applied to the liquid crystal display by the opposite end of shaft 12, which in turn squeezes liquid crystal layer 17 sandwiched between glass plates 16a, 16b, thereby clouding the display. An operator can detect changes in pressure by noting the degree of clouding of liquid crystal layer 17.
Nevertheless, a device employing a spring such as is shown in FIG. 1 is not suitable for miniaturization because it requires sufficient space for displacement of the spring to indicate operation force or pressure. Furthermore, the device shown in FIG. 2 which employs an electronic circuit requires a power source to operate the circuit, for which purpose a battery is usually employed. Consequently, even should miniaturization be attempted by using an IC as the electronic circuit, there remains the problem that space is still required for a battery, rendering such a device unsuitable for miniaturization. In addition, relative to the accuracy of indication of the operation force or pressure, such a device entails a high production cost.
Finally, in the device shown in FIG. 3 which uses pressure applied directly against a liquid crystal display, because pressure is indicated only by the degree of clouding of the liquid crystal, indication is unstable and the degree of applied pressure difficult to read.